In my opinion, the most important human invention is not an artefact, such as the pill or the electric shaver. It's an idea, the very idea that made all these technical successes possible: the concept of education.
Our brain is nothing but a collection of networks of neurons and synapses that have been shaped by evolution to solve specific problems. Yet through education and culture, we have found ways to "recycle" those networks for other uses. With the invention of reading and writing, we recycle our visual system to do word reading. With the invention of mathematics, we apply our innate networks for number, space, and time to all sorts of problems beyond their original domain of relevance. Education is the key invention that enables all these rewirings to take place at a time when our brains are still optimally modifiable.
As David Premack likes to remind us, homo sapiens is the only primate that has invented an active pedagogy. Without education, it would only take one generation for all the inventions that other have mentioned to vanish from the surface of the earth.